The dopaminergic neurons of the mesolimbic dopamine (DA) system projecting from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) are a common target for many drugs of abuse, and are thought to play a central role in the development of addiction. Recently, several studies have suggested that one endogenous neurochemical that serves to regulate these DA neurons is acetylcholine (ACh);however, direct evidence characterizing this modulation in intact animals is lacking, due largely to the absence of methods for monitoring in vivo ACh at sufficiently high spatial and temporal resolution. Thus, the studies described in this proposal are designed to characterize the cholinergic modulation of mesolimbic DA transmission by monitoring neurochemicals at both ends of this projection in separate experiments (that are not dependent on one another) using fast-scan cyclic voltammetry (FSCV) at carbon fiber microelectrodes. This electrochemical approach is well suited for real-time measurements of chemical changes in the brain, due to the excellent temporal and spatial resolution afforded by the technique. Electrochemical data will be analyzed with principal component regression, allowing individual chemical components to be objectively distinguished and selectively quantitated. The specific aims involve both the development of new technology (Aim 1) and innovative applications of existing analytical and neurobiological methods (Aim 2). They are: 1. The development and characterization of a novel electrochemical detection method for ACh that can be used to rapidly monitor fluctuations of this neurochemical in the VTA. 2. A quantitative study of how cholinergic compounds in the VTA modulate the temporal dynamics of dopamine efflux in the NAc of an awake animal. A better understanding of the cholinergic regulation of naturally occurring DA transmission may reveal a novel set of chemical mechanisms and physiological pathologies affecting the brain's reward system. PUBLIC HEALTH RELEVANCE: Drug abuse and addiction are significant problems in the United States. Estimates of the total overall costs of substance abuse in the United States-including health- and crime-related costs as well as losses in productivity-exceed half a trillion dollars annually. The dopaminergic neurons of the mesolimbic dopamine system projecting from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) are a common target for many drugs of abuse, and are thought to play a central role in the development of addiction. The focus of this research is to understand how the endogenous neuromolecule acetylcholine can act at dopamine cell bodies to regulate dopamine release from the terminals. This work may reveal a novel set of chemical mechanisms and physiological pathologies affecting the brain's reward system.